The long-term goal of proposed research is to understand the physiological role of zinc finger protein ZPR1 in the pathogenesis of spinal muscular atrophy (SMA) caused by mutation of the survival motor neurons (SMN1) gene. SMA is characterized by degeneration of the spinal motor neurons. The cellular and molecular mechanisms of neuron degeneration are unclear and no treatment is available for SMA. The defect in nuclear accumulation of SMN is the biochemical defect in SMA. ZPR1 is required for nuclear accumulation of SMN in sub-nuclear bodies, including gems and Cajal bodies. The severity of SMA correlates negatively with SMN containing nuclear bodies. The severity of SMA may be influenced by the actions of modifier genes. One potential modifier gene is represented by ZPR1, which is down regulated in patients with SMA. The reduced expression of ZPR1 causes axonal defects and loss of spinal motor neurons in mice. The proposed research will determine the function of ZPR1 in the growth and differentiation of neurons and role of ZPR1 as a protective modifier of SMA. We will test the hypothesis that the increased expression of ZPR1 may ameliorate the severity of SMA disease and the ZPR1 gene may be a protective modifier of SMA. The Specific Aims of the research project are: Aim 1. To examine the physiological function of ZPR1 in neurons. We will examine the effect of ZPR1 deficiency in neurons (A) in vitro using cultured primary neurons, including spinal cord motor neurons from conditional Zpr1 (F1/F1) knockout mice and inactivation of the Zpr1 gene by infection with adenovirus expressing Cre recombinase. (B) In vivo by crossing conditional Zpr1 (F1/F1) mice with transgenic Hb9-cre mice expressing Cre recombinase under the control of endogenous mouse Hlxb9 promoter. Aim 2. To examine the effect of ZPR1 overexpression on the severity of disease and rescue of the SMA phenotype. (A) by generating a transgenic mouse overexpressing FLAG-ZPR1 under the control of a mouse ROSA26 promoter. We will examine the effect of ZPR1 overexpression on the growth and differentiation of neurons and growth and development of mice. (B) We will examine the effect of ZPR1 overexpression on severity and rescue of the SMA phenotype by crossing SMA model mice with transgenic Flag-Zpr1 mice. The phenotype of SMA mice with ZPR1 overexpression will be examined. Aim 3. To examine the role of ZPR1 in stabilization and nuclear accumulation of SMN. We will examine the cellular and molecular mechanisms of stabilization of SMN and nucleocytoplasmic trafficking of ZPR1 and SMN complexes. We will examine the role of cytoplasmic and nuclear proteins that interact with ZPR1 and may mediate nuclear export/import of ZPR1 and SMN. We will examine the role of phosphorylation and prolyl cis-trans isomerization that may regulate nucleocytoplasmic trafficking of ZPR1-SMN complexes. We will examine the effect of ZPR1 deficiency on the stability and integrity of SMN complex, nuclear accumulation of SMN and snRNP biogenesis. The findings of proposed study will provide insights into the function of ZPR1 in the nuclear accumulation of SMN and pathogenesis of SMA.